Survival analysis and biochemical response of the juvenile Nile tilapia (Oreochromis niloticus) exposed to metalaxyl fungicides

The study examined the biochemical parameters and behavioral changes of Oreochromis niloticus exposed to different concentrations of metalaxyl fungicide using a survival analysis model. Batches of ten O. niloticus were randomly distributed into a set of 18 rectangular plastic tanks (75×45×45cm) each filled with 30L of unchlorinated water. The range-finding tests for metalaxyl (400, 500, 600, 700, and 800 ml) were carried out for 24h, and the definitive test (500, 600, 700, 800, and 900 ml) for 96h. At the end of 96h exposure of O. niloticus to metalaxyl, blood samples (5mL) were collected through the vertebral caudal blood vessel into sample bottles for biochemical analysis. The acute toxicity 96h LC₅₀ was calculated to be 7.41 ml, while mortality rate and death prediction were determined using survival analysis. There was a significant increase (p>0.05) in the activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), as well as the levels of protein, cholesterol, and creatinine. Abnormal behavior such as fin deformation, air gulping, loss of reflex, molting and erratic swimming was observed in the experimental fish. Survival analysis results revealed that the average survival hour at 50% of events was 72h. The survival rate declines with an increase in the concentration and the chance of survival gets worse between 700 ml and 900 ml concentrations. The survival of fishes is significantly influenced by the concentrations at different levels at a time in point. However, alterations were seen in biochemical parameters and behavioral responses clearly indicate that the occurrence of metalaxyl in freshwater bodies, even in minute concentrations, could cause lethal effects on the biochemical parameters of fish and may threaten their survivability in the natural environment. Therefore, control measures should be taken to prevent the possible contamination of the aquatic environment by metalaxyl fungicide.